1. Field of the Invention
This invention relates to catalyst components for use in the polymerization of olefinic hydrocarbons. The invention is also directed to a process for the manufacture of olefinic polymers in which the aforesaid catalyst components are employed.
2. Prior Art
Catalyst compositions comprising zirconium compounds, typically metallocene, and alumoxane are known for use in the homopolymerization of olefins such as ethylene or the copolymerization of ethylene/alpha-olefins as disclosed for example in Japanese Laid-Open Patent Publication No. 58-19309. While the disclosed prior art process is advantageous so far as concerns the availability of polymerized products at increased rate of yield, it has a drawback in that the polymers obtained have a relatively low molecular weight and further that they, if homopolymeric, have a relatively narrow molecular weight distribution. When taking into account the molecular weight alone, it would be possible to increase the molecular weight of a polymer to some extent by making a proper selection of transition metals from among the group of metallocene. It has been proposed to use dicyclopentadienyl hafnium as disclosed for example in Japanese Laid-Open Patent Publication No. 63-251405. However, hafnium compounds are not only difficult to synthesize but also less active compared to dicyclopentadienyl zirconium. The use of dicyclopentadienyl hafnium would not provide any appreciable increase in the breadth of molecular weight distribution of the polymer produced, or would not help in providing sufficiently narrow composition distribution of the polymer when the latter is a copolymer.